EF0 tornado, Moorland Nesler Arpt, Iowa, July 11, 2011

1. EF065 to 85 mphthis tornado

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mph

   Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

4. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 mph

   Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

7. Unrated

   The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

Rating

EF0

Date

July 11, 2011

Touchdown

2:52 AM CDT (07:52 UTC)

Lifted

2:56 AM CDT (07:56 UTC)

On the ground

4 minutes

Path length

2.2 miles (3.6 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

Crop damage

$10,000

County

Webster County

Touchdown point

42.427, -94.288

Lift-off point

42.432, -94.246

Record number

1107110152-01

A very unstable airmass was in place over Iowa with CAPE values around 6000 J/kg and lifted indices around -11 C. The downdraft CAPE was 1500 to 1900 J/kg. CAPE in the -10 to -30 C layer of the atmosphere was high, in the 800 to 1200 J/kg range, however the freezing level was 15,500 feet, limiting the hail production. The shear profile was relatively weak with 30 kts of effective shear available. Predawn temperatures were in the upper 70s to around 80, with dewpoints in the mid 70s. Precipitable water values were in the 1.5 to 2 inch range, boosted by a 35 kt low level jet. Thunderstorms formed in two complexes along a weak frontal boundary extending from Minnesota into Kansas. One of the complexes pushed north and east out of Kansas and Nebraska, the second was over southern Minnesota. The two filled in during the night as the whole system moved into richer air. An outflow boundary was located across northern Iowa from the complex in Minnesota, enhancing convection there. As the storms moved into Iowa, the primary threat came in the form of wind with wind gusts of 40 to 60 MPH associated with the fast moving forward propagating MCS. Wind damage occurred in the Atlantic area with a tree blocking U.S. Highway 6. This cluster of storms continued to move across the state at around 55 MPH. Wind damage occurred in the Des Moines area with tree branches down and power line damage caused by 60 MPH winds. A 59 MPH wind gust was recorded at the Ames Airport as the storms passed. As the complex of storms continued east out of central Iowa, widespread damage occurred across Marshall and Tama Counties with winds of 70 to 100 MPH. Two radio towers were downed, one in central Tama County, the other in northern Polk County. A local television station's weather radar was destroyed near Alleman, also in Polk County. Local wind speeds in these areas were estimated as high as 115 MPH. Widespread power outages were reported with 90% of the power still out in Marshall County, and 75% out in Tama County 12 hours after the event. Power was out for 3 to 4 days in some places. Governor Terry Brandstad gave a State Disaster Proclamation to Story, Marshall, and Tama Counties due the extensive damage. A presidential declaration for major disaster was also given to Story, Marshall, and Tama Counties. A broad area of severe damage occurred with a path 5 miles wide of EF1 type damage caused by the high winds. A path, 10 miles wide, of 70 to 80 MPH was surveyed, with a 15 to 20 mile wide path of wind speeds above 60 MPH. The damage swath was nearly continuous with no evidence of tornadoes. It extended from southern Story and northern Polk Counties, through Marshall, and Tama Counties, and was about 75 miles in length before exiting the CWA. Crop losses were substantial with around 40% or greater loss on over 100,000 acres of corn and soy beans. The corn had much more damage than the bean plants, with damage on these acres estimated at $95,000,000. Other damage occurred around the area as well. This derecho event was the most widespread one to affect central and east central Iowa since the June 1998 event. Some examples of the notable wind speeds estimated from the survey include 96 MPH near Huxley, 94 MPH near Maxwell, 70 to 90 MPH near Marshalltown, 105 MPH east of Garwin, 85 to 97 MPH between Garwin and Union Grove State Park, 100 MPH south of Traer, and south to southwest of Dysart 105 to 115 MPH, with 80 to 100 MPH winds just south of that part of the swath. One dairy farmer near Dysart reported the total loss of 300 acres of corn and $300,000 damage to the farm. Several of his dairy cows perished or had to be euthanized. The farmer said he would have to go out of the farming business after 45 years due to the extent of the loss. In Tama County, officials reported that 1000 county road signs were destroyed by the high wind. Meanwhile, the northern part of the system continued to produce strong winds with a 63 MPH wind gust reported at the Fort Dodge Airport.

An intermittent path captured by photographs from an airplane. The narrow path was entirely in fields of corn and soybeans as it moved nearly due east.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.

The county was under a severe thunderstorm watch, issued at 06:21 UTC and running to 08:53 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Slight Risk. The outlook in force was issued at 05:45 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

The Des Moines radar (KDMX), 90 km away, was scanning. The volume nearest the touchdown began at 07:51 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2011 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.